Evolution: Natural Selection, Mutation, and Speciation
Understanding Evolution: Key Concepts and Theories
Reproduction, Asexual Source Variability
Variability: Generates gene recombination during meiosis and random union of gametes during fecundation.
Selection Pressure and Adaptation
Factors that adversely affect individual survival constitute selection pressure. Adaptation arises from the pressure of natural selection.
Evidence for Evolution
Evidence supporting the theory of evolution comes from multiple fields:
- Anatomical Studies: Organisms are studied according to body structures to establish parental relationships:
- Homologous structures have the same underlying structure, but may or may not have the same function.
- Analogous structures have the same function but different origins.
- Vestigial structures are those whose function has been lost over time.
- Paleontology: The study of fossils. Fossils bear similarities to current species.
- Embryology: Comparative study of embryonic development in different animals. Similarities fade as the process progresses.
- Biogeography: Study of species’ geographic distribution. Organisms living together in similar environments evolve similarly.
- Biochemistry: Comparison of different organisms at the molecular level. The more similar two species are at the molecular level, the closer their evolutionary relationship.
Neo-Darwinism
Neo-Darwinism:
- Rejects Lamarckism.
- States that genetic variability is due to mutation and recombination.
- Natural selection acts on genetic variation.
- Natural selection leads to changes in the allele frequencies of a population.
- Populations, not individuals, evolve.
- Evolution occurs gradually.
Punctuated Equilibrium
Balanced Point: Not all evolutionary changes are gradual. This concept was proposed by Niles Eldredge and Stephen Jay Gould.
Species and Speciation
Species: A cluster of genes that share the same set and can create fertile offspring.
Speciation: Processes leading to the formation of a new species from pre-existing ones.
Common Ancestors
The human species is the sole representative of the hominid family. Hominids, apes, monkeys (New World and Old World primates), and prosimians share common ancestry.
Bipedalism
Walking on two feet without hand support.
Hypotheses on the Origin of Life
- Panspermia: Life originates in space, traveling in the form of spores to other planetary systems.
- Prebiotic Synthesis: Life arises from organic molecules that emerged on an inorganic planet.
Precursor Cells
Oparin proposed that molecular reactions in the primordial soup led to simple organic molecules joining together. These molecular associations occurred in the form of spheres, hollow and containing nucleic acids.
Biological Evolution
Biological Evolution: The process by which species change over time.
- Fixism: The belief that species have remained unchanged.
- Evolution: Species can change and generate new species.
Lamarckism
The first theory of evolution. Lamarck believed that species transformed into other species continuously over time. Key points:
- Organisms have a tendency towards complexity.
- Repeated use of an organ leads to its development.
- Acquired characteristics are heritable.
Darwinism
Developed by Charles Darwin and Alfred Russel Wallace. There is no intrinsic tendency that forces species to evolve in a certain way. Evolution is an open, endlessly determined process.
Evolution by Natural Selection
Darwin and Wallace proposed natural selection as the mechanism by which species change over time. Darwin drew a parallel to artificial selection practiced by farmers in improving breeds. Key points:
- There is a struggle for survival among organisms.
- Variability exists among individuals of a population.
- The environment selects the organisms best adapted.
Mutations: Source of Variability
Mutations are random disturbances in genes. Mutations affecting gametes are transmitted to offspring.
- Harmful mutations: Cause a handicap or death to the individual.
- Beneficial mutations: Provide an advantage, enhancing the individual’s survival capacity.
- Neutral mutations: Neither beneficial nor harmful.
Mutations generate heritable variation.